1. Field of the Invention
The present invention relates to a method and apparatus for applying flux for use in brazing aluminum or an aluminum alloy (which are collectively called as "aluminum material") and is employed for in the manufacture of various products (for example, a radiator or a condenser).
The present application is based on Japanese Patent Applications No. Hei. 10-214485, 10-214488, 10-239172 and 10-239175, which are incorporated herein by reference.
2. Description of the Related Art
For example, in the case of manufacture of a heat exchanger from aluminum material, heat-transfer tubes made of aluminum material and radiation fins made of aluminum material are assembled, and the assembly is heated in a heating furnace, thereby fusing brazing filler metal (an aluminum alloy containing 5-16% Si) that is interposed beforehand between the heat-transfer tubes and the radiation fins. The heat-transfer tubes and the fins are brazed by means of the brazing filler metal.
In order to achieve high-quality brazing between the heat-transfer tubes and the radiation fins, fluoride-based flux is applied to the portions of the tubes and fins which are to be brazed, so as to fracture an oxide film covering the surface of the aluminum material constituting the heat-transfer tubes and the radiation fins.
The fluoride-based flux comprises 65.6-99.9 wt. % KAlF.sub.4 and 34.4 to 0.1 wt. % K.sub.3 AlF.sub.6 and is commercially available under the trade name NOCOLOK FLUX.
A method of applying this flux is described in Japanese Patent Publication Nos. Hei. 1-143796, Hei. 3-275272 and Hei. 4-322896 or the like.
Japanese Patent Publication No. Hei. 1-143796 describes a method whereby flux can be applied solely to areas requiring coating by use, as a dispersion medium, of polybutene whose viscosity is greater than that of water and which sublimes with an increase in temperature. Japanese Patent Publication No. Hei. 3-275272 describes industrially efficient manufacture of an aluminum heat exchanger by coating of flux, which includes polybutene as a dispersion medium, to a traveling coating belt and by transfer of the flux to the surface of aluminum material from the coating belt.
Neither of these patent coatings specifically discloses correlation between the amount of flux added to polybutene and means for applying the flux. The former publication describes only the amount of flux added to polybutene but contains no description of a measure for applying the flux. The latter patent publication describes only means for applying flux and contains no description about the amount of flux added to polybutene.
Further, coating material of the above slime-like flux is applied primarily by manual paint with a brush. Accordingly, the amount of flux applied on the surface of a component becomes non-uniform, for example, such as on the tope peaks of a corrugated component used in the core of the heat exchanger. Further, during a painting process, flux is splashed, thereby staining surrounding facilities.
With regard to coating material formed by addition of flux into polybutene, the viscosity of the coating material increases with an increase in the amount of flux contained in the coating material. Consequently, coating material containing a small amount of flux has low viscosity and, hence is applicable to a spraying method or a dipping method. However, such coating material is not suitable for a transfer method employing an coating belt. On the other hand, coating material containing a large amount of flux has high viscosity and, hence can be applied to a transfer method employing an coating belt as coating means. However, such coating material is not suitable for a spraying method or a dipping method.
As mentioned above, in connection with the method of applying flux for use in brazing aluminum material, a close correlation exists between the amount of flux added to polybutene and means for applying the flux.
The present inventor found that most of the areas requiring coating of flux are narrow and that coating material doped with flux is required to have high viscosity for adherence to the narrow areas after coating. On the basis of this finding, the present inventor has completed the present invention.
Incidentally, a core of a heat exchanger, such as an evaporator or a condenser, employed in an automobile cooling system is usually constituted by stacking in an alternating manner a plurality of corrugated outer fins and a plurality of flat coolant tubes into a layer of required width. After the ends of the respective coolant tubes of the core are inserted into tube insertion holes formed in header tanks, powder flux or a flux solution is sprayed onto the overall core, whereby the flux adheres to the core. This core is then heated in a heating furnace, to thereby braze together the top peaks of the corrugated outer fins and the coolant tubes remaining in contact with the outer fins.
Flux adheres to areas of the core other than the areas to be brazed, thus wastefully consuming flux and disadvantageously adding to cost. Further, splashing of flux deteriorates the working environment and stains surrounding facilities.